The invention pertains to guideway operated vehicular systems and, more particularly, to improved methods and apparatus for controlling and propelling vehicles utilizing linear synchronous motors. The invention has application in people movers and materials transport systems, to name but a few.
A Linear Synchronous Motor (LSM) can be used to propel vehicles in a wide variety of systems for transporting people and goods. The type of LSM most appropriate for these missions is the “long stator” version in which the stator, or primary, runs the entire length of the guideway and the vehicle, or secondary, is much shorter and moves in close proximity to the stator. In order to handle multiple vehicles it is necessary to divide the guideway into regions that are typically referred to as “blocks” and to provide a separate power control system for each block. Such a power control system typically includes a power source (in the case of an LSM, a variable frequency, variable voltage, multi-phase source) and a controller (microprocessor-based or otherwise) with position sensing, e.g., to adjust the inverter to insure proper vehicle operation. Throughout this application, the power control system of an LSM is referred to as an “inverter.”
A common prior art configuration of the power control system of an LSM is to have a separate inverter for each block. An example of an implementation of this power control scheme is shown in U.S. Pat. No. 3,158,765, Magnetic system of transportation. That patent shows a power control scheme that is similar to FIG. 1 hereof. As a vehicle enters each block, the inverter for that block is activated (e.g., by the associated controller) for powering the moving vehicle while it is within that block. Simple block switching of this type is satisfactory if the vehicles are not too close and the power dissipation in the stator is not too large.
In the case of transportation systems where the vehicles travel long distances with considerable distance between vehicles and especially when the force is relatively large, the prior art teaches the use of “sub-block switching”. Examples of this are illustrated in U.S. Pat. No. 4,068,152, Power Supply System for a Linear Motor, and U.S. Pat. No. 5,361,707, Multiple feeder system of feeder sections for feeding ground coils of superconductive magnetically levitated railway. These patents show a power control scheme as generally shown in FIG. 2 hereof wherein each block is be divided into multiple sections, each of which is coupled to one of a bank of inverters for that block by an associated switch. As a vehicle enters each block, the appropriate inverter for that block is activated and the associated switches are used to couple power from it to those sections of the block in which the moving vehicle is located.
Prior art sub-block switching schemes take advantage of the fact that a switch is considerably less expensive than an inverter. There are many ways to implement sub-block switching and some of these are described in U.S. Pat. No. 4,454,457, Power supply system for a linear motor, and U.S. Pat. No. 4,955,303, Linear motor feeder system.
A problem with sub-block switching is that it does not permit propulsion and control of multiple vehicles which are closely spaced. As an example, it is not suitable for elevator applications of the LSM where two or more cabs operate in the same hoistway and have to move independently, even stopping on adjacent floors anywhere in a building. Nor, by way of further example, is it suitable for transit system applications, where it is desirable to have short spacing between vehicles in and near stations. In instances such as these, it is not necessary to have close spacing everywhere along the guideway, however, such need does exist at specific locations.
An object of the invention is to provide improved linear synchronous control systems and methods. A further object of the invention is to provide such systems and methods for use in guideway operated vehicles.
A still further object of the invention is to provide such systems and methods as permit independent powering and/or control of closely spaced vehicles—even in instances where multiple vehicles are in a single block.
A related object of the invention is to provide such systems and methods as can also be used where vehicles are not so closely spaced.